#Number of Elements in Circular Queues and Simple Queues #Doubt

Question

How many elements a simple queue and a circular queue both of size N can accommodates ?

( A )  N and N respectively.

( B )  N-1 and N-1 respectively.

( C )  N and N-1 respectively.

( D )  N-1 and N respectively.

Answer 1

It depends largely on the implementation. I am assuming that in your question N refers to the size of the array used to implement these queues (and not the size of queues themselves).

Now for normal queue, we can easily use the complete array for queue use, i.e. having N elements, using a rear and a front pointer.

Now, for the circular queue, we need a condition for checking if the Q is full and for checking if the Q is empty. For empty, we usually use front == rear, since when both the pointers point at the same location the Q is empty. And for checking if Q is full, we use rear+1 mod N == front. Using these ways we can only use N-1 elements in the Q. So, answer C.

But, there are some clever ways to use all the N elements in the circular Q. Like using a flag to denote Q is empty or full. Think about it!!! Answer can be A.

Comments

Yes True. The answer is A. Instead of using front and rear pointer to determine whether the queue is full or empty in the circular queue. We can simply use count variable.

Count = 0 represent circular queue is empty.
Count = N represent circular queue is full.

Answer 2

is not it N and N respectively.

But array index should be Q[0]-> Q[N-1]

A

Answer 3

A simple queue can accommodate N elements

But circular queue can accommodate (N-1) elements because of the conditions QUEUE FULL and QUEUE EMPTY